Wireless communication systems are widely deployed to provide various communication services such as voice, video, packet data, messaging, broadcast, etc. These wireless systems may be multiple-access systems capable of supporting multiple users by sharing the available system resources, e.g., time, frequency, power. Examples of such multiple-access systems include Code Division Multiple Access (CDMA) systems, Time Division Multiple Access (TDMA) systems, Frequency Division Multiple Access (FDMA) systems, Orthogonal FDMA (OFDMA) systems, and Single-Carrier FDMA (SC-FDMA) systems.
A wireless communication system may include a number of base stations that can support communication for a number of mobile terminals. The system may support operation on multiple carriers. Each carrier may be associated with a particular center frequency and a particular bandwidth. Each carrier may carry pilot and overhead information to support operation on the carrier. Each carrier may also carry data for terminals operating on the carrier. Some transmissions between a terminal and a base station may cause interference to, and may also observe interference from, other transmissions in the communication system. The interference may adversely impact the performance of all affected base stations.
Typically, in two-way conversations, each party speaks for sometime during which a communication system transmits the party's speech (e.g., less than half of the time) and pauses for other times during which the communication system transmits silence or background noise. Infrequent transmission or discontinuous transmission (DTX) during the silence (or background noise) period has little impact on the perceptual quality of the conversation but provides the benefits of reducing inter-/inter-cell interference (therefore potentially increasing the system capacity) and conserving the battery power of a mobile unit used for the conversation.
A typical DTX scheme is realized by a speech encoder that uses voice activity detection (VAD). Using VAD, the encoder can distinguish active speech from background noise. The encoder encodes each active speech segment (typically 20 ms long) with a target bit rate packet for transmission and represents critical background noise segments (again 20 ms long) with a relatively small size packet. This small packet may be a silence descriptor (SID) indicating silence. A critical background noise segment might be the background noise segment that immediately follows a talk spurt, or a background noise segment whose characteristics are significantly different from its precedent noise segments. Other types of background noise segments (or non-critical background noise segments) are denoted with 0 bits, or blanked, or not transmitted, or suppressed from transmission. Because the pattern of output packets (namely active segment(s) then critical background noise segment(s) then non-critical background noise segment(s)) purely depends on the input of the speech encoder, or the source, such a DTX scheme is called a source-controlled DTX scheme.